1. Field of the Invention
The present invention relates to an organic electro-luminescent (EL) display, and more particularly, to a dual-panel type organic EL display and a method for manufacturing the same.
2. Discussion of the Related Art
Generally, dual-panel type organic EL displays include a lower substrate, on which pixel switching elements and pixel driving elements are formed, and an upper substrate, on which an organic material is laminated. The upper and lower substrates are bonded to be electrically connected, for implementation of a display.
Hereinafter, a conventional method for manufacturing such a dual-panel type organic EL display will be described.
The lower substrate of a dual-panel type organic EL display mainly includes, for each pixel region thereof, a switching thin film transistor (typically, a polysilicon thin film transistor) for switching of a pixel corresponding to the pixel region, a driving thin film transistor for driving of the pixel, a storage capacitor, and a pixel electrode.
FIG. 1A is a sectional view illustrating a conventional process for manufacturing a lower substrate of a dual-panel type organic EL display. The following description will be given only in conjunction with one thin film transistor included in one pixel of the dual-panel type organic EL display.
In accordance with the conventional process, first, a semiconductor layer 2 made of, for example, polysilicon, is formed over a transparent substrate 1, as shown in FIG. 1A. The semiconductor 2 is then patterned such that the semiconductor 2 remains only in a region where a thin film transistor is to be formed.
Thereafter, a gate insulating film 3 and a conductive film for formation of a gate electrode are sequentially formed over the entire surface of the resulting structure. The conductive film is then patterned to form a gate electrode 4.
Using the gate electrode 4 as a mask, impurity ions such as phosphorous (P) ions are then implanted into the semiconductor layer 2 which is, in turn, annealed to form source and drain regions 2a and 2c of the thin film transistor. Thus, an NMOS thin film transistor is completely formed.
The portion of the semiconductor layer 2, into which the impurity ions are not implanted, forms a channel region 2b of the NMOS thin film transistor.
Next, an interlayer insulating film 5 is formed over the entire surface of the resulting structure. Subsequently, the interlayer insulating film 5 and gate insulating film 3 are selectively removed such that the source and drain regions 2a and 2c of the NMOS thin film transistor are exposed.
An electrode line 6 and a pixel electrode 6′ are then formed on the exposed source and drain regions 2a and 2c such that the electrode line 6 and pixel electrode 6′ are electrically connected to the source and drain regions 2a and 2c, respectively. Thus, the lower substrate is completely formed.
FIG. 2 is a plan view illustrating an upper substrate of the dual-panel type organic EL display manufactured in accordance with a conventional process. FIG. 1B is a cross-sectional view taken along the line I-I of FIG. 2.
In accordance with the conventional process, as shown in FIGS. 1B and 2, an anode 8 is formed on a transparent substrate 7. The anode 8 is made of a transparent conductive material having a high work function, such as indium tin oxide (ITO) or indium zinc oxide (IZO).
Thereafter, an insulating film 9 is formed on a portion of the anode 8, using an insulating material such as polyimide. A barrier 10 is then formed on the insulating film 9.
Next, an island-shaped spacer 11 is formed on the anode 8 at a pixel region, using another insulating material.
Subsequently, organic materials for a hole injection layer 12, a hole transfer layer 13, a light-emitting layer 14, an electron transfer layer 15, and an electron injection layer 16 are sequentially deposited over the entire surface of the resulting structure including the spacer 11.
A cathode 17, which is made of a conductive material having a low work function, such as aluminum, is then deposited over the electron injection layer 16. Thus, the upper substrate is completely formed.
FIG. 1C is a sectional view illustrating a process for bonding the lower substrate of FIG. 1A and the upper substrate of FIG. 1B.
As shown in FIG. 1C, the lower substrate of FIG. 1A and the upper substrate of FIG. 1B are bonded such that the cathode 17 formed on the spacer 11 in the upper substrate comes into contact with the pixel electrode 6′ to be electrically connected.
FIG. 1D is a sectional view illustrating a process for sealing the organic EL display in which the upper and lower substrates are bonded. As shown in FIG. 1D, vacuum is formed in a space defined between the bonded upper and lower substrates. Thereafter, the space between the upper and lower substrates is sealed, using a sealant 18.
In the conventional organic EL display manufactured in the above-mentioned manner, NMOS thin film transistors must be used because each cathode in the upper substrate and the drain region of the corresponding driving thin film transistor in the lower substrate are electrically connected.
However, the above-mentioned conventional EL display has a problem in that it is difficult to use a low-temperature polysilicon thin film transistor manufacturing process using a laser annealing method. This is because the low-temperature polysilicon thin film transistor is of a PMOS type.
For this reason, the conventional organic EL display cannot use PMOS thin film transistors which are more stable than NMOS thin film transistors.